To meet demands for faster processors and higher capacity memories, integrated circuit (IC) designers are focusing on decreasing the minimum feature size within integrated circuits. By minimizing the feature size within an integrated circuit, device density on an individual chip increases exponentially, as desired, enabling designers to meet the demands imposed on them. As modem silicon devices become smaller and the minimum feature size of CMOS (complementary metal oxide semiconductor) devices approaches and goes below the 0.1 μm regime, very thin gate insulators of thickness less than 2 nm (20 Å) will be required to keep the capacitance of the DRAM (dynamic random access memory) capacitor cell in the range of 30 fF. This capacitance value is generally required to provide immunity to radiation, soft errors and a nominal signal-to-noise ratio.
Silicon dioxide (SiO2), the most commonly used insulator, shows high leakage current density at thicknesses in the range of 20 nm due to band-to-band tunneling current or Fowler-Nordheim tunneling current. As a result, high-k dielectric films such as aluminum oxide (Al2O3), tantalum pentoxide (Ta2O5) and titanium dioxide (TiO2) have received considerable interest as gate insulators to replace silicon dioxide.
While aluminum oxide has shown considerable promise, its porous nature leads to drawbacks. It has been noted that aluminum oxide porosity is generally the result of an acicular crystalline structure and that some pores may extend through the entire thickness of an aluminum oxide layer having a thickness on the order of 100 nm. Studies have also shown that exposure to humid atmospheres and even normal atmospheric conditions leads to a build-up of water in the pores of aluminum oxide films. This water build-up results in a loss of dielectric properties. In particular, water build-up can lead to a decrease in breakdown voltage of several orders of magnitude.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative aluminum oxide structures and methods of their production.